Jellyfish lifespans typically range from a few hours (in the case of some very small hydromedusae) to several months. Life span and maximum size varies by species. One unusual species is reported to live as long as 30 years. Another species, Turritopsis dohrnii as T. nutricula, may be effectively immortal because of its ability to transform between medusa and polyp, thereby escaping death.

The Turritopsis Nutricula is able to revert back to a juvenile form once it mates after becoming sexually mature. Marine biologists say the jellyfish numbers are rocketing because they need not die.

While most members of the jellyfish family usually die after propagating, the Turritopsis nutricula has developed the unique ability to return to a polyp state. Scientists believe the cycle can repeat indefinitely, rendering it potentially immortal.

Wow! That's amazing. The Daily Telegraph article was dated last January. How did I miss that?

Naked Scientist Forum’s intrepid researcher John Chapman has done the leg work so that you don’t have to.

Jellyfish generally have a complex life cycle. A mature individual takes the form of a medusa (jelly fish). It’s eggs and sperm form a larva called a planula which is a single celled ciliate plankton. This then develops into a hydroid like creature with branches ending in polyps. Numerous new miniature medusa are budded from within the polyps which in due course become sexually mature and produce new eggs and sperm.

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According to the latest (8th) edition of the book ‘Developmental Biology’, by Scott F Gilbert, the life cycle of Turritopsis nutricula has evolved a remarkable variation on this theme:

”How does Turritopsis accomplish this feat? It can do this because it can alter the differentiated state of a cell, transforming it into another cell type. Such a phenomenon is called transdifferentiation, and it is usually seen only when parts of an organ regenerate. However, it appears to occur normally in the Turritopsis life cycle (Figure below). In this transdifferentiation process, the medusa is transformed into the stolons and polyps of a hydroid colony. First, the umbrella everts and the tentacles and mesoglea (the middle layer) are resorbed. The everted medusa attach to the substrate by the end that had been at the opposite end of the umbrella, and spawning occurs shortly thereafter. The cnidarian then secretes a perisarc (stolon covering) and stolons. Two days after the stolons are first seen, polyps differentiate. These polyps feed on zooplankton and soon are budding off new medusae.”

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Turritopsis nutricula is the first reported case of an organism which is capable of reverting back completely to a sexually immature stage after having reached sexual maturity. Thus, it appears that it has cheated death and is potentially immortal.

What myriam really wants to know is what the mechanism of this revertion is and can this developmental pathway be exploited to allow immortality in humans? Wouldn’t it be strange if, after many years of aging into an elderly person we could then flip some biochemical switch and grow backwards into babies, only to repeat the cycle again and again. You’re not alone, myriam. You, me and the rest of the world want to know the same thing.

yes, I know seems to be impossible to repeat life cycle of a human being but that doesn't mean that there are some people not trying to make them self like immortal, did you heard about cryonics , it is crazy!! but a reality.

well, I mean, we can learn from those mechanisms to try to regenerate cells, taking the example of nervous cells...